1. Field of the Invention
The present invention relates to a node device for transferring supervisory control information in a photonic network having various network topology configurations such as ring interconnection, mesh connection or the like for accommodating and transmitting signals for various services.
2. Description of the Related Art
Conventionally, a network topology configuration in the photonic network system has employed a point-to-point configuration. However in recent years, the construction of the photonic network systems employing the ring topology and the mesh topology are studied in which the OADM (Optical Add/Drop Multiplexing) node and the HUB node for realizing the path switching of the signal as the light without the photoelectric conversion are used.
Also, the OTN (Optical Transport Network), the Ethernet (registered trademark), the FC (Fiber Channel) and the like have been added to the types of the signals to be transmitted in the photonic network in addition to the SONET (Synchronous Optical Network)/SDH (Synchronous Digital Hierarchy) which have been transmitted in the photonic network conventionally. Accordingly, the variety of the types of the signals to be transmitted in the photonic network has become wider.
The photonic network consists of an optical transmission/reception terminal station, an optical HUB node device, and an optical amplification relay device for the WDM (Wavelength Division Multiplexing) signals, and optical fibers which are the transmission lines for connecting the above node devices, for example.
Each node device comprises an EMS (Equipment Management System) for operating and managing the devices, and each EMS is connected to a NMS (Network Management System) for integrating and managing the photonic network. The supervisory control information transferred to each node device is managed by the NMS or the EMS.
Also, in the photonic network, the optical path switch control is conducted in the unit of the wavelength path in which the optical wavelength of each signal is used as the unit for the path. In each wavelength path, the information is transmitted, for example, in the format of the SONET, the SDH, the OTN, the Ethernet (registered trademark), the FC or the like.
As the method for transferring the supervisory control information for each wavelength path, there are two major methods as below (see Patent Document 1 below for example).
Patent Document 1
Japanese Patent Application Publication No. 09-247106
(1) Dedicated Wavelength Method
Dedicated wavelength which is out of signal wavelength band of WDM signal is assigned for supervisory control, and each node device transfers supervisory control information while providing electrical termination of the supervisory control information. This dedicated wavelength is referred to as OSC (Optical Supervisory Channel) and used for transferring supervisory control information of the WDM signal by n channel multiplexing.
(2) Main Signal Superposition Method
In an optical transmission terminal station of each wavelength path, supervisory control information with the bit rate sufficiently lower than the bit rate of optical main signal is modulated by subcarrier, and then, the supervisory control information is transferred being superposed on the optical main signal.
FIG. 1A shows an example of a photonic network in accordance with the above dedicated wavelength method. This network consists of transmission terminal stations 11-1 and 11-2, a HUB node device 12 and reception terminal stations 13-1 and 13-2.
The transmission terminal station 11-1 comprises an EMS 21-1 and a transmitter (OSC-S) 22-1, and the transmission terminal station 11-2 comprises an EMS 21-2 and a transmitter (OSC-S) 22-2. A reception terminal station 13-1 comprises an EMS 21-4 and a receiver (OSC-R) 23-3, and a reception terminal station 13-2 comprises an EMS 21-5 and a receiver (OSC-R) 23-4.
Also, the HUB node device 12 comprises an EMS 21-3, receivers (OSC-R) 23-1 and 23-2, transmitters (OSC-S) 22-3 and 22-4, and an optical path switch 24. The OSC-S and the OSC-R are the transmitter and the receiver for the supervisory control information in accordance with the dedicated wavelength method, respectively. The supervisory control signals are generated/terminated in respective node devices.
Signal light 31 in a wavelength path A sent from the transmission terminal station 11-1 and signal light 32 in a wavelength path B sent from the transmission terminal station 11-2 are transmitted to the reception terminal station 13-2 via the optical path switch 24 of the HUB node device 12.
Upon this, the EMS 21-1 generates supervisory control information 33 for the wavelength path A on the OSC, transfers the generated information to the EMS 21-3 via the transmitter 22-1 and the receiver 23-1. The EMS 21-2 generates supervisory control information 34 for the wavelength path B on the OSC and transfers the generated information to the EMS 21-3 via the transmitter 22-2 and the receiver 23-2. The EMS 21-3 transfers the received supervisory control information 33 and 34 to the EMS 21-5 via the transmitter 22-4 and the receiver 23-4.
As described above, in the dedicated wavelength method, the path switching for the supervisory control information is conducted similarly to that for the optical main signal in the HUB node device 12.
FIG. 1B shows an example of a photonic network in accordance with the above described main signal superposition method. This network consists of transmission terminal stations 51-1 and 51-2, a HUB node device 52, and reception terminal stations 53-land 53-2.
The transmission terminal station 51-1 comprises an EMS 61-1, a receiver (SC-Ro) 63-1 and a plurality of transmitters (SCM), and the transmission terminal station 51-2 comprises an EMS 61-2, a receiver (SC-Ro) 63-2 and a plurality of transmitters (SCM). The reception terminal station 53-1 comprises an EMS 61-4 and a receiver (SC-Ri) 64-3, and a reception terminal station 53-2 comprises an EMS 61-5 and a receiver (SC-Ri) 64-4.
Also, the HUB node device 52 comprises an EMS 61-3, receivers (SC-Ri) 64-1 and 64-2, receivers (SC-Ro) 63-3 and 63-4, and an optical path switch 65. The SCM is a transmitter for the supervisory control information in accordance with the main signal superposition method, and superposes the supervisory control signal on the optical main signal for each wavelength path. The SC-Ro and the SC-Ri are the receivers in accordance with the main signal superposition method, and extract the supervisory control information superposed on the optical main signal.
Signal light 71 in the wavelength path A sent from the transmission terminal station 51-1 and signal light 72 in the wavelength path B sent from the transmission terminal station 51-2 are transmitted to the reception terminal station 53-2 via the optical path switch 65 of the HUB node device 52.
Upon this, the EMS 61-1 generates supervisory control information 73 for the wavelength path A, and the transmitter 62-1 superposes the supervisory control information 73 on the optical main signal in the wavelength path A. Similarly, the EMS 61-2 generates supervisory control information 74 for the wavelength path B, and the transmitter 62-2 superposes the supervisory control information 74 on the optical main signal in the wavelength path A. As above, in the main signal superposition method, the supervisory control information is superposed on the optical main signal to be transferred.
The above conventional method of transferring supervisory control information has problems as below.
In the HUB node device in the photonic network, the path switch control is conducted in a device by using a MEMS (Micro Electro Mechanical Systems) switch and a wavelength selection switch so that each wavelength path input via an arbitrary route on the input side which is connected to the corresponding device is connected to a desired route on the output side.
In the dedicated wavelength method upon this, in order that each wavelength path and the supervisory control information for the corresponding wavelength path are connected to the same route on the output side, the path switching control has to be conducted both on the optical main signal in the wavelength path and the supervisory control information for the corresponding wavelength path. However, in the dedicated wavelength method, the optical main signal and the supervisory control information for each wavelength path are transmitted respectively having different wavelengths from each other, accordingly, a device for confirming that both of them correspond to each other and are connected to the same route on the output side is required.
To the contrary, in the main signal superposition method, the optical main signal in each wavelength path and the supervisory control information for the corresponding wavelength path are transmitted having the same wavelengths with each other, accordingly, it is not necessary to confirm whether or not both of them correspond to each other as above.
However, in the main signal superposition method, a bit rate of the supervisory control information has to be sufficiently lower than that of the optical main signal, so that the bit rate of the supervisory control information is generally in the range of several hundred bps to several kbps in the order. Accordingly, the transmission rate of the supervisory control information is limited.
Also, in many cases in the main signal superposition method, the supervisory control information can be generated only by the transmission terminal station in each wavelength path and it is difficult to update the supervisory control information in the node devices through which each wavelength path is transmitted as shown in FIG. 1B. Therefore, the main signal superposition method is not suitable for transferring the supervisory control information which has to be updated along the route of the wavelength path.